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1   /*
2    * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2006 Daniel Le Berre
3    * 
4    * Based on the original minisat specification from:
5    * 
6    * An extensible SAT solver. Niklas E?n and Niklas S?rensson. Proceedings of the
7    * Sixth International Conference on Theory and Applications of Satisfiability
8    * Testing, LNCS 2919, pp 502-518, 2003.
9    * 
10   * This library is free software; you can redistribute it and/or modify it under
11   * the terms of the GNU Lesser General Public License as published by the Free
12   * Software Foundation; either version 2.1 of the License, or (at your option)
13   * any later version.
14   * 
15   * This library is distributed in the hope that it will be useful, but WITHOUT
16   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17   * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
18   * details.
19   * 
20   * You should have received a copy of the GNU Lesser General Public License
21   * along with this library; if not, write to the Free Software Foundation, Inc.,
22   * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
23   * 
24   */
25  package org.sat4j.minisat.core;
26  
27  /**
28   * Utility methods to avoid using bit manipulation inside code. One should use
29   * Java 1.5 import static feature to use it without class qualification inside
30   * the code.
31   * 
32   * In the DIMACS format, the literals are represented by signed integers, 0
33   * denoting the end of the clause. In the solver, the literals are represented
34   * by positive integers, in order to use them as index in arrays for instance.
35   * 
36   * <pre>
37   *  int p : a literal (p&gt;1)
38   *  p &circ; 1 : the negation of the literal
39   *  p &gt;&gt; 1 : the DIMACS number reresenting the variable.
40   *  int v : a DIMACS variable (v&gt;0)
41   *  v &lt;&lt; 1 : a positive literal for that variable in the solver.
42   *  v &lt;&lt; 1 &circ; 1 : a negative literal for that variable. 
43   * </pre>
44   * 
45   * @author leberre
46   * 
47   */
48  public final class LiteralsUtils {
49  
50      private LiteralsUtils() {
51          // no instance supposed to be created.
52      }
53  
54      public static int var(int p) {
55          assert p > 1;
56          return p >> 1;
57      }
58  
59      public static int neg(int p) {
60          return p ^ 1;
61      }
62  }